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Go to the profile of Ferhan Sagin
Jul 04, 2018

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Go to the profile of Athel Cornish-Bowden

This recommendation worries me, because the book revives some misconceptions that were found in most biochemistry textbooks when I first started teaching biochemistry, but which have gradually faded in the past half-century. For example, in the 4th edition of White, Handler and Smith (1968) the authors make it clear that they don't really believe in dipolar ions (zwitterions): they introduce amino acids with wrong (neutral) structures. After several pages of wrong structures they include a brief mention of dipolar ions, perhaps put in at the pedantic insistence of a physical chemist, and then return to wrong structures for the rest of the book. This was very common in 1970, but is relatively rare now, found only in the least satisfactory textbooks. Unfortunately the book recommended in the post perpetuates the misconception. Why does it matter? If students think of glycine, for example, as a molecule that combines the properties of acetic acid (a strongly smelling and reactive liquid) and ethylamine (a strongly smelling and reactive gas) how can they understand why it looks and behaves like a salt?

As a different example, in 1970 most textbooks showed the curve representing the rate of an enzyme-catalysed reaction obeying Michaelis-Menten kinetics as "reaching" the maximum velocity at about 5Km, though a simple calculation shows that 5/6 is much less than 1. Most authors have learned better since then, but the author this book is not one of them, and even shows the curve reaching saturation at about 3Km.

Go to the profile of Angel Herráez
Angel Herráez about 23 hours ago

I agree with Dr. Cornish-Bowden argument, as a desirable approach to address descriptions even from the introductory levels of biochemistry. I believe it is not uncommon to find these pitfalls in other sources, and a case might be made of tolerating such inaccuracies in favour of some simplification or when the stress is on some other aspects of the subject. It is, nonetheless, much better to provide in any case the most accurate representations, particularly to avoid misconceptions being seeded in the student brain.

However, I find the discredit not fair in this case. Checking the text, "Biochemistry Free For All", version 1.2 [1], the first introduction to "General amino acid structure" (Figure 2.1) does indeed present the carboxylic and amino groups uncharged (which may be claimed to be a better introductory illustration of the definition as amino+acid compound), but immediately in the next figures all the 20 amino acids are presented as zwitterionic structures (pages 59-61 , figures 2.3 to 2.7). And, subsequently, all the different equilibria and ionised forms for a single amino acid are shown along its titration curve (fig. 2-10). In the accompanying PowerPoint file [2], the structures are again first displayed uncharged but immediately as zwitterions.

Coming to the Michaelis & Menten curve, it is true that the drawing of the hyperbola in many places is often wrong in making the curve reach the asymptote at far too low concentrations of substrate. I remember myself fighting against these displays; fortunately, they are becoming less common now in highly accessed places like Wikipedia [3]. Once again, I do not see this is the case with Ahern's book. Some plots (fig. 4.18, p. 349) do not label the [S] axis with any values (as it also happens in other textbooks, e.g. Stryer [4]), while the one that quotes numeric values in the axes (fig.4.20, p.351 and slide 31 in ref.5) seems to be mathematically accurate, displaying 90% saturation at [S] = 9.75 times Km.

Cited references:



[3] Confront, for example,ética_de_Michaelis-Menten with–Menten_kinetics

[4] Berg JM, Tymoczko JL, Stryer L (2002) Biochemistry, 5th ed.